Device for gioniometric measurements

ABSTRACT

A device ( 1 ) for measuring the relative orientation according to at least one degree of freedom for two objects, including a constraint generator ( 10 ) suitable for causing a goniometric sensor ( 40 ) to move in a plane, having the function of measuring the variation of relative orientation of the two objects in this plane. The goniometric sensor ( 40 ) is arranged in a housing ( 41 ) that crosses longitudinally the constraint generator ( 10 ), which has high flexional stiffness in a first longitudinal plane (β) and a low flexional stiffness in a second longitudinal plane (φ) orthogonal to the first (β) . The sensor measures rotations in a plane and the constraint generator induces a rotation in that plane. With the device ( 1 ) a data suit ( 50 ) can be made for measuring the movement of limbs of an individual. For example, arranging three devices ( 10   a,    10   b,    10   c ) in series, but capable of measuring angles in orthogonal planes, the rotation can be measured of the arm ( 76 ) with respect to a shoulder ( 75 ) of an individual.

FIELD OF THE INVENTION

The present invention generally relates to a device for determining theangular position of an object.

In particular, the invention relates to a device for determining therelative angular position between two objects articulated to each otherwith at least one degree of freedom.

Furthermore, the invention relates in particular, but not exclusively,to a device for determining the relative angular position of two limbsof the human body, for example the arm and the shoulder, the forearm andthe arm, the wrist and the elbow, etc.

BACKGROUND OF THE INVENTION

The angular movements between objects that have one or more degrees offreedom are measurable with complex devices of various structure ofmechanical, optical, electromagnetic nature, etc.

One of the fields in which the angular measures are very important isthat of the study of the posture of the human body by measure andcontrol of absolute position data of single points of the body or ofangular relative position of two adjacent limbs. On the basis of thedata recorded a digital model of the human body is then created.

Many are the possible applications, such as the production of digitalmovies or virtual reality, as well as applications in the medical field,and deserve a space of primary importance in scientific research.

However some limits exist that define substantially the fields ofapplicability for each type of device. Such limits are given mainly tothe size of the limb that has to be monitored and to the number ofdegrees of freedom of the limb same.

In particular, the limbs with greater volume, such as arms and legs,have less degrees of freedom and the devices used for detecting theirmotion have larger weight and encumbrance and require a higher rate ofprecision. The limbs with smaller volume, such as the fingers of thehands, have a higher number of degrees of freedom and the devices usedfor detecting their motion must have lower weight and encumbrance andrequire a lower rate of precision.

The least expensive devices for detecting the movement of the limbs withgreater volume are of mechanical type. They provide the use of rigidparts connected with rotational and prismatic joints, measuring angularmovements with potentiometers. Even if the costs of this technology arelow, however the rigid structure has high encumbrance, it is heavy andthe measures obtained are usually not so precise.

Also magnetic sensors exist, which-require one or more transmitters forcreating a magnetic field in a determined workspace. However, they havehigh costs and have the further drawback of being particularly affectedby the presence of metal that can distort the magnetic field.

The optical sensors, finally, require optical tracers, active orreflective, whose light is captured by cameras for then analysing theposition data by means of a computer. Usually, the optical devices areless bulky of the magnetic, but their correct operation can be affectedby parts of the body that cross accidentally the light path. Otherdrawbacks of the optical devices are high costs and the need forpost-processing the measured data as well as the long set-up time forthe measuring equipment.

Another system of “motion capture” for the human body is described inU.S. Pat. No. 6,050,962. It provides angular sensors of resistive typeor “resistive bend sensors” arranged at the joints, associated toauxiliary articulated connections formed by a plurality of links hingedin turn. The links form a chain that can rotate in a single plane.Consecutive portions of chain can rotate in different planes connectedto each other by stiff or articulated junction elements. The angularsensors are in particular resistive segments that measure the rotationsof the limbs to which they are applied, or of portions of them. Theresulting device is structurally complex and expensive.

SUMMARY OF THE INVENTION

It is therefore object of the present invention to provide a device formeasuring the relative orientation of at least a first object withrespect to a second object, in particular but not exclusively limbs ofthe human body, which is structurally easy and not expensive to make,and that does not present the drawbacks of the prior art.

It is another object of the present invention to provide such a devicethat is light and has low encumbrance.

It is a further object of the present invention to provide such a devicethat is capable of measuring the angular rotation with sufficientprecision.

These and other objectives are accomplished by the device for measuringthe relative orientation of at least a first object with respect to asecond object free from said first object, or connected to it but withindependent movement, wherein said orientation is carried out accordingto at least one degree of freedom comprising:

-   -   at least one goniometric sensor for said or each degree of        freedom suitable for measuring the variation of orientation in a        plane;    -   at least one constraint generator for said or each goniometric        sensor for causing the latter to move in said plane;

whose characteristic is that said or each constraint generator is anelongated flexible element, having a longitudinal axis, with a flexionalstiffness remarkably lower in a first plane passing through the saidaxis and a flexional stiffness remarkably higher in a second planeorthogonal to said first plane and passing through the said axis,whereby said element is substantially flexible only in said first plane.Furthermore, said flexible element has also high stiffness to torsionand to elongation.

In particular, the goniometric sensor measures the relative angularmovement of the two objects in the bending plane of the constraintgenerator.

Advantageously, said or each goniometric sensor is located in a housingthat crosses longitudinally said constraint generator.

Alternatively, the sensor is made in the flexible element same.

Advantageously, said or each constraint generator has a plurality ofsubstantially parallel portions having larger cross section alternatedto portions coaxial to the previous but with smaller cross section.

In a first embodiment, at the portions having smaller cross sectionflexible elements are arranged, or lamellar hinges, suitable forallowing the mutual rotation of said portions having larger crosssection only in the bending plane of the constraint generator.

Alternatively, said or each constraint generator is a plate shapedelement from which projections extend substantially bellow-like. Inparticular, said bellow-like projections have structure chosen among:helical; alternated annular portions having larger and smaller crosssection.

Preferably, the constraint generator has flanges at its ends orthogonalto said axis for connecting more constraint generators 1 in series orfor connecting to the objects whose rotation must be detected.

Preferably, the goniometric sensor for measuring the relative rotationof the ends of said constraint generator comprises:

-   -   a flexible elongated element that extends between said ends,        said element having a neutral axis which does not change its own        length when bending, and at least one fibre spaced apart from        said neutral axis and that extends from said first to said        second object;    -   means for measuring the length variation of said fibre as the        relative rotation varies between said first and said second        object, said relative rotation being proportional to said length        variation.

According to a particular aspect of the invention, when said firstobject can rotate about more axes with respect to said second object,the use is provided of a plurality of constraint generators connectedrigidly in series at the respective ends and in particular a constraintgenerator for each axis of rotation, or rotational degree of freedom,and oriented according to different planes of flexion, so that eachsensor present in the corresponding constraint generator measures thebending in a different plane. In this case the relative rotationalmovement of the first object with respect to the second object iscomputed combining the measures of angular movements in each flexionplane.

This solution can be used, for example, if the movement has to bemeasured of the shoulder of an individual with respect to another pointof the body. In this case, considering the rotational constraint of thearm with respect to the shoulder as a ball joint, a device can be usedfor measuring the rotation of the arm with respect to the shouldercomprising in series three constraint generators integrated to threegoniometric sensors according to the invention. The first has a free endintegral to the shoulder and is oriented for bending in a first plane,the second in a second plane orthogonal to the first and the third in athird plane orthogonal to the second with its free end integral to thearm.

Moreover, a device for measuring the rotation of the forearm withrespect to the arm comprises a constraint generator and a relativegoniometric sensor, with an end integral to the arm and the other endintegral to the forearm.

A particular aspect of the invention relates to a device for measuringthe rotation of the wrist of an arm comprising at least one goniometricsensor as above described. In particular, said or each goniometricsensor is arranged with an end integral to the wrist and with the otherend constrained to a second point of the arm that during the rotation ofthe wrist remains substantially fixed, for example to the elbow.Therefore, the goniometric sensor measures the rotation of the wristwith respect to the second point of the arm.

According to another particular aspect of the invention, a data suit formeasuring the angular rotation of the arm with respect to the shoulder,of the forearm and of the wrist with respect to the arm of an individualcomprises:

-   -   a device for measuring the rotation of the arm with respect to        the shoulder as above described;    -   a device for measuring the rotation of the forearm with respect        to the arm, as above described, arranged orthogonally to said        device for measuring the rotation of the arm with respect to the        shoulder;    -   a device for measuring the rotation of the wrist, as above        described, having an end rigidly connected to said device for        measuring the rotation of the forearm with respect to the arm.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and the advantages of the device according tothe present invention will be made clearer with the followingdescription of an embodiment, exemplifying but not limitative, withreference to the attached drawings, wherein:

FIG. 1 shows a top plan view of a constraint generator according to theinvention;

FIG. 2 shows a longitudinal sectional view according to arrows II-II ofthe constraint generator of FIG. 1;

FIG. 3 shows an elevational side view of the constraint generator ofFIG. 1;

FIG. 4 shows an elevational front view of the constraint generator ofFIG. 1;

FIG. 5 shows a perspective view of the constraint generator of FIG. 1;

FIG. 6 shows a perspective view of a different embodiment of theconstraint generator of FIG. 1;

FIG. 7 shows a top plan view of the constraint generator of FIG. 6;

FIG. 8 shows a longitudinal sectional view according to arrows VIII-VIIIof FIG. 7 of the constraint generator of FIG. 6;

FIG. 9 shows a longitudinal sectional view according to arrows IX-IX ofFIG. 8 of the constraint generator of FIG. 6;

FIG. 10 shows a top plan view of a not helical embodiment of theconstraint generator of FIG. 6;

FIG. 11 shows a top plan view of three constraint generators rigidlyconnected and oriented on orthogonal bending planes, so that each sensorpresent in the relative constraint generator measures the bendingoccurring in the corresponding plane;

FIG. 12 shows a top plan view of a device for measuring the angularrotation of the wrist and of the forearm with respect to the arm,according to the invention;

FIGS. 13 and 14 show respectively in a perspective view and a top planview a data suit for measuring the angular rotation of the arm withrespect to the shoulder, of the forearm and of the wrist with respect tothe arm of an individual, according to the invention;

FIG. 15 shows a longitudinal sectional view of a possible embodiment ofa goniometric sensor suitable for being arranged in the constraintgenerator of FIG. 1 or of FIG. 6;

FIG. 16 shows diagrammatically in a perspective elevational side viewthe data suit of FIG. 12 that an individual has put on;

FIGS. 17 to 19 show a perspective view of a possible embodiment of adevice for measuring the rotation of the wrist, according to theinvention.

DESCRIPTION OF A PREFERRED EMBODIMENT

In FIGS. 1 to 5 a device 1 is shown, according to the invention, formeasuring the relative orientation according to at least one degree offreedom of two separated objects, or connected objects but havingindependent movement. It comprises a constraint generator 10 suitablefor causing a goniometric sensor 40 to move in a plane for measuring thevariation of relative orientation of the two objects in that plane.

As shown in the cross sectional view of FIG. 2, goniometric sensor 40 isarranged in a housing 41 that crosses longitudinally constraintgenerator 10. A type of goniometric sensor is shown in FIG. 15, anddescribed hereinafter.

With reference to FIG. 5, constraint generator 10 has a longitudinalaxis 8 and is equipped with a high flexional stiffness when bending in afirst plane β passing through that axis 8 and a low flexional stiffnesswhen bending in a second plane φ orthogonal to plane β and passingthrough axis 8 same. Therefore, constraint generator 10 is flexible onlyin plane φ and goniometric sensor 40 measures the relative angularmovement of the two objects in this plane.

Always with reference to FIG. 1, constraint generator 10 has a pluralityof substantially parallel portions having larger cross section 2alternated to a plurality of portions coaxial to the previous havingsmaller cross section 3. In particular, the portions having smallercross section 3 allow bending and cause the mutual rotation of theportions having larger cross section 2 only in bending plane φ ofconstraint generator 10. In particular, narrower zones 3 are made aslamellar hinges that extend in or parallel to plane β, and then allowbending only in plane φ. At the ends fastening flanges 5 a and 5 b areprovided, for either connecting the constraint generators 1 in seriesaccording to orthogonal planes, or connecting the constraint generatorsto the objects whose rotation must be detected.

In an alternative embodiment of the invention and shown in FIGS. 6 to10, constraint generator 10 can comprise a plate-shaped portion 6, withlarger dimensions parallel to plane β and lower dimension in plane φ.From plate-shaped portion 6 substantially bellow like projections 2extend that are arranged helically in axial direction. At the end ofplate 6 fastening flanges 5 a and 5 b orthogonal to plate 6 same can be,furthermore, provided.

Alternatively, as shown in FIG. 10, the bellow-like shape is obtained bya plurality of rings alternated of diameter higher 2 and lower 3 thatproject from plate 6.

In both cases, plate-shaped portion 6 has flexional stiffness remarkablyhigher in plane β, and can bend in plane φ to it orthogonal.Furthermore, the bellow like structure increases the torsionalstiffness.

The constraint generator according to the invention in the variousembodiments, and made in other equivalent ways, can be manufactureddirectly by moulding in a single element of plastics.

In FIG. 15 in a longitudinal sectional view a possible embodiment ofgoniometric sensor 40 is shown. On sensor 40 a neutral axis 100 in caseof bending does not change its own length, and with numeral 105 a lineis indicated eccentric to the neutral axis. When the two objects ofwhose relative orientation has to be determined rotate reciprocally,then flexible elongated element 42 is subject to a bending that producesa length variation of the fibres not located at neutral axis 100. Inparticular, the fibre located at eccentric line 105 is subject to alength variation ΔL. This length variation of fibre 105 can bedetermined by means of a sensor 47, for example a Hall effect sensor,which detects the movement of a cable 45 located in a channel 44 made inthe element end 42. In particular, sensor 47 measures the movement of amagnet 46 connected to an end of cable 45 and sliding in an enlargedportion 44 a of channel 44.

The goniometric sensor can be inserted after the moulding of theconstraint generator or embedded in the plastic matrix of the constraintgenerator. In a further embodiment, the goniometric sensor is madedirectly in constraint generator 10, carrying out a measure oflengthening of a fibre different from the neutral axis of constraintgenerator 10 same, in a way similar to the goniometric sensor shownabove.

The type of goniometric sensor used, obviously, is exemplifying and notlimitative, and goniometric sensors of other type can be used capable ofmeasuring the rotation of the two ends of constraint generator 10.

According to a particular aspect of the invention, if the orientationhas to be measured of a first object capable of rotating about threeaxes with respect to a second object, the use is provided of threeconstraint generators 10 connected rigidly in series at the ends 5 (FIG.11). In particular, the three constraint generators 10 are orientedaccording to the different bending planes, so that each sensor 40present in the corresponding constraint generator 10 measures thebending in a different plane. Therefore, the relative rotationalmovement of the first object with respect to the second object iscomputed, in this case, combining the measures of angular movements ineach flexion plane.

This solution can be, for example, used for measuring the movement ofarm 76 of an individual with respect to the shoulder (FIG. 16). In thiscase, considering the movement of the arm with respect to the shoulder75 as a spherical movement characterised by 3 independent degrees offreedom, such rotations are measurable with device 50 for measuring therotation of arm 76 with respect to shoulder 75, comprising the threeconstraint generators 10 in series and the relative three goniometricsensors 40 to it associated.

Always with reference to FIG. 16, first constraint generator 10 a has afree end 5 a integral to shoulder 75 and is oriented for bending in afirst plane. Second constraint generator 10 b has end 5 a rigidlyconnected to end 5 b of first generator 10 a and is oriented for bendingin a second plane orthogonal to the first flexion plane. Thirdconstraint generator 10 c has in turn an end 5 a rigidly connected toend 5 b of second generator 10 b, it is oriented for bending in a thirdplane orthogonal to the second bending plane and has the free end 5 bconnected to a support 80 integral to arm 76 by means of a belt 81.

Similarly, a device 20 for measuring the rotation of forearm 77 withrespect to arm 76 comprises a constraint generator 10 and a relativegoniometric sensor 40. In this case, a first end 5 a of constraintgenerator 10 is mounted on a support 80 integral to arm 76 by means of abelt 81 and the other end 5 b is fixed to a support 82 integral toforearm 77 by means of a belt 83 (FIG. 16). Finally, if at end 5 b ofdevice 20 a rod 31 is connected, as detailed in FIGS. 17 to 19, having afree end at the wrist 65 and provided with a goniometric sensor 40 (withor without constraint generator), it is possible to measure also therotation of the wrist 65 with respect to arm 76.

Notwithstanding reference has been made mainly to the movement of an armwith respect to a shoulder, a forearm and a wrist, the above mentioneddevice can be easily implemented by a skilled person for measuring themotion of other parts of the body such as legs, head, trunk, etc.

The foregoing description of a specific embodiment will so fully revealthe invention according to the conceptual point of view, so that others,by applying current knowledge, will be able to modify and/or adapt forvarious applications such an embodiment without further research andwithout departing from the invention, and it is therefore to beunderstood that such adaptations and modifications will have to beconsidered as equivalent to the specific embodiment. The means and thematerials to realise the different functions described herein could havea different nature without, for this reason, departing from the field ofthe invention. It is to be understood that the phraseology orterminology employed herein is for the purpose of description and not oflimitation.

1. Device for measuring the relative orientation of at least a firstobject with respect to a second object free from said first object, orconnected to it but with independent movement, wherein said orientationis carried out according to at least one degree of freedom comprising:at least one goniometric sensor for said or each degree of freedomsuitable for measuring the variation of orientation in a plane; at leastone constraint generator for said or each goniometric sensor for causingthe latter to move in said plane; characterised in that said or eachconstraint generator being a flexible elongated element having alongitudinal axis with a low flexional stiffness in a first planepassing through the said axis and a high flexional stiffness in a secondplane orthogonal to said first plane and passing through the said axis,whereby said element is flexible only in said first plane.
 2. Device,according to claim 1, wherein said constraint generator has highstiffness to torsion and to tensile stress.
 3. Device, according toclaim 1, wherein said or each goniometric sensor is located in a housingthat crosses longitudinally said constraint generator, said goniometricsensor measuring the relative angular movement of said objects in abending plane of said constraint generator.
 4. Device, according toclaim 1, wherein said or each constraint generator has a plurality ofsubstantially parallel portions having larger cross section alternatedto a plurality of portions with smaller cross section, whereby suchsmaller cross sections confer to the structure a big flexional capacityin a plane and in the meantime a big flexional stiffness in a planeorthogonal to it, as well as a big stiffness to torsion and to tensilestress.
 5. Device, according to claim 1, wherein said or each constraintgenerator is an plate shaped element from which projections extendsubstantially bellow-like.
 6. Device, according to claim 5, wherein saidbellow-like projections have structure chosen among: helical; alternatedannular portions having larger and smaller cross section.
 7. Device,according to claim 1, wherein said constraint generator has flangesorthogonal to said axis for fastening at its ends more constraintgenerators 1 in series or for fastening to the objects whose rotationmust be detected.
 8. Device according to claim 1, wherein saidgoniometric sensor comprises: a flexible elongated element that extendsbetween a first and a second object, said element having a neutral axis,which does not change its own length when bending, and at least onefibre spaced apart from said neutral axis and that extends from saidfirst to said second object; means for measuring the length variation ofsaid fibre as the relative rotation varies between said first and saidsecond object, said relative rotation being proportional to said lengthvariation.
 9. Device for measuring the relative orientation of a firstobject capable of rotating about more axes independent with respect to asecond object characterised in that it comprises a plurality ofconstraint generators, according to claim 1, connected rigidly in seriesat the ends, and in particular a constraint generator for each axis ofrotation or rotational degree of freedom, said constraint generatorsbeing oriented according to the different flexion planes, so that eachsensor present in the corresponding constraint generator measures thebending in a different plane, said relative rotational movement of saidfirst object with respect to said second object being determined bymeans of a combination of measures of angular movements in each flexionplane.
 10. Device for measuring the rotation of the arm with respect tothe shoulder of an individual characterised in that it comprises threeconstraint generators, according to claim 1, arranged in seriesassociated to three goniometric sensors, wherein the first constraintgenerator has a free end integral to the shoulder and is oriented forbending in a first plane, the second constraint generator in a secondplane orthogonal to the first and the third constraint generator in athird plane orthogonal to the second and having the free end integral tosaid arm..
 11. Device for measuring the rotation of the forearm withrespect to the arm of an individual characterised in that it comprises aconstraint generator and a relative goniometric sensor, according toclaim 1, with an end integral to the arm and the other end integral tothe forearm.
 12. Device for measuring the rotation of the wrist of anindividual with respect to a point of the arm, which point during therotation of the wrist remaining substantially fixed, characterised inthat it comprises at least one goniometric sensor according to claim 8arranged with an end integral to the wrist and with the other endconstrained to said fixed point, said goniometric sensor measuring therotation of the wrist with respect to said second point of the arm. 13.Data suit for measuring the angular rotation of the arm with respect tothe shoulder, of the forearm and of the wrist with respect to the arm ofan individual characterised in that it comprises a device for measuringthe rotation of the arm with respect to the shoulder according to claim10; a device for measuring the rotation of the forearm with respect tothe arm, arranged orthogonally to said device for measuring the rotationof the arm with respect to the shoulder; a device for measuring therotation of the wrist, comprising at least one goniometric sensorarranged with an end integral to the wrist and with the other endconstrained to said fixed point, said goniometric sensor measuring therotation of the wrist with respect to said second point of the arm.